This invention in general relates to an improved air filter structure for use with carburetors. The improved air filter reduces the restriction to air flow reaching the carburetor over prior art air filters.
It is known in the prior art to have venturi-type air intake ports in carburetors which draw fuel through discharge ports into the air flow. Such carburetors have found particular success in racing vehicles. One well-known type of such carburetors is the Holley.TM. Carburetor.
In this basic type of carburetor, air is drawn into the carburetor through venturi ports. A central boost venturi surrounds a fuel discharge nozzle, which communicates with a fuel bowl in the carburetor. As air flows through the venturi, it draws fuel into that air flow through the discharge ports.
The central boost venturi is typically centered within the main air venturi. The boost venturi, as a venturi within a venturi, "sees" a lower absolute pressure (or higher vacuum) than the main venturi. To increase this effect, the fuel discharge in the boost venturi may be placed at the point of lowest pressure in the main venturi. This may be typically achieved by placing the boost venturi in a throat of the main venturi.
In designing the dimensions and contours of the main venturi, the boost venturi, and the fuel discharge force, several competing factors are considered. Engineering on the dimensions and contours of such carburetor is sufficiently advanced such that the dimensions and contours are typically optimized for each particular application.
As an example, a small venturi provides high velocities, strong metering signals, good atomization, vaporization, and mixing of the fuel and air. However, a large venturi is less restrictive to air flow, increasing air flow and the engine's power potential. At the same time, a larger venturi provides less effective atomization at low engine speeds.
The amount of air drawn into the engine through the carburetor has a direct effect on the available power from the engine. Typically, the amount of available air flow to the engine is always less than is desired. That is, it is always generally desired to increase the potential air flow. However, as explained above, due to various competing factors, one may not simply change the structure of the carburetor to increase the air flow.
At the same time, it is always necessary to filter the air leading to the engine and carburetor. In the absence of efficient filtering of impurities from the air, the engine will not be able to operate for any appreciable length of time.
In racing applications, it is particularly desirable to achieve maximum power, and thus supply as much air as possible to the carburetor. This goal, however, conflicts with filtering of the air. Prior art air filters typically restrict the air flow to the carburetor by as much as twenty percent over "free air flow." The term "free air flow" is used here to describe the amount of air that would flow through the carburetor in the absence of an air filter. Obviously, the restriction of twenty percent of the air flow leading to the carburetor is an undesirable result of the use of an air filter. At the same time, an air filter is a necessity.
While compromises that reduce potential air flow in the carburetor structure are inevitable, as explained above, the same compromise of reduced air flow due to the use of an air filter should be minimized to the extent possible. The prior art has been faced with the conflicting factors of the necessity of filtering the air, while at the same time desirably increasing air flow through the carburetor. The two goals have not both been satisfactorily met at this time.